Solvent extraction with internal preparation of stripping steam

ABSTRACT

A solvent extraction process for effecting the separation of polar hydrocarbons from a mixture thereof with non-polar hydrocarbons. Water, from which steam is generated and utilized to strip hydrocarbons from the extract phase, is internally prepared within the process and is substantially free from nonpolar hydrocarbons.

llaite States atent Van Tassell SOLVENT EXTRACTION WITH INTERNAL [75]Inventor: Harry M. Van Tassell, Arlington Heights, Ill.

[73] Assignee: Universal Oil Products Company,

Des Plains, lll.

[22] Filed: Nov. 23, 1973 [2]] Appl. No.: 418,698

[52] U.S. Cl 208/321, 208/325, 208/333 [51] Int. Cl Cl0g 21/28 [58]Field of Search 208/321 [56] References Cited UNITED STATES PATENTS3,173,966 3/1965 Jones et al. 208/321 PREPARATION OF STRIPPING STEAM[451 Feb. 4, 1975 3,492,222 1/1970 Van Tassel] 208/321 3,714,033 1/1973Somekh et a1. 208/321 Primary Examiner-Herbert Levine Attorney, Agent,or Firm-James R. Hoatson, Jr.; Robert W. Erickson; William H. Page 11 Asolvent extraction process for effecting the separation of polarhydrocarbons from a mixture thereof with non-polar hydrocarbons. Water,from which steam is generated and utilized to strip hydrocarbons fromthe extract phase, is internally prepared within the process and issubstantially free from non-polar hydrocarbons.

ABSTRACT 8 Claims, 1 Drawing Figure Ex/racr Receiver Solvent StripperPATENTED 41975 no 386m \mimumm \mmcxla SOLVENT EXTRACTION WITH INTERNALPREPARATION OF STRTPPING STEAM APPLICABILITY OF INVENTION The inventionherein described is adaptable for utilization in the separation, andultimate recovery of polar hydrocarbons from a mixture thereof withnon-polar hydrocarbons, which separation is effected through the use ofa solvent characteristically selective for adsorbing the polarhydrocarbons. More specifically, my invention involves the separationand recovery of aromatic hydrocarbons from various mixtures thereof withnon-aromatic hydrocarbons, which process utilizes an internally preparedwater stream, substantially free from non-aromatic hydrocarbons, togenerate the steam which is employed in a solvent-stripping zone for thepurpose of recovering an aromatic concentrate substantially free fromthe selected solvent and nonaromatic hydrocarbons.

In the present specification and appended claims, the use of the termspolar and non-polar is intended to distinguish between classes ofhydrocarbons wherein one particular type is more polar while another isless polar. For example, in the extraction of aromatics from a mixturethereof with naphthenes and paraffins, the latter are considerednon-polar with respect to aromatics which are polar." In one of itsspecific applications, the process encompassed by the present inventiveconcept serves to segregate particular species of aromatic hydrocarbons,such as benzene, toluene and- /or C aromatics from other hydrocarbonsnormally contained in petroleum fractions and/or distillates. Theprocess utilizes a solvent which may be indefinitely recycled within thesystem, yields the desired hydrocarbon products in high purity, andseparates the same substantially in its entirety from the feed stockscharged to the process.

The present invention is particularly directed toward an improvement inthe type of separation process wherein a mixture of various classes ofhydrocarbons is introduced into a solvent extraction zone, beingcounter-currently contacted therein with a solvent selective foraromatic hydrocarbons. A raffinate phase, comprising substantially allof the non-aromatic hydrocarbons in the feed stock, is removed from anend portion of the extraction zone, an extract phase comprising thearomatic components of the charge stock is removed from the other endportion of the extraction zone, with the aromatic solute being recoveredin a solvent stripping zone through the utilization of steam.

Although my invention is applicable for use with any hydrocarbon feedstock having a sufficiently high aromatic concentration to justify therecovery thereof-i.e., at least about 25.0 percent by volume-significantadvantages are afforded when processing those charge stocks having anaromatic hydrocarbon concentration at least about 65.0 percent byvolume. The overall carbon number range of suitable charge stocks isfrom about six to about 10. These charge stocks will generally include,in addition to C C and C aromatics, non-aromatics which predominate in Cand C paraffins and naphthenes. Exemplary of various sources of suitablecharge stocks are the depentanized effluent from a naphtha catalyticreforming unit, coke oven byproducts, wash oils, hydrotreated pyrolysisnaphtha, etc.

My inventive concept involves a unique procedure for the internalpreparation of a water stream from which steam is generated forutilization in the solvent stripping zone. Internal preparation" isintended to connote that the water stream is prepared within thephysical confines of the solvent extraction process. The presenttechnique has many advantages over currentlypracticed prior artprocedures. Among these is a decrease in the quantity of non-polarhydrocarbons introduced into the stripping zone, in turn resulting in apolar hydrocarbon product of increased purity. Other advantages arehereinafter discussed, and will become evident to those possessing therequisite skill in the appropriate art.

PRIOR ART Candor compels recognizing that the prior art is replete witha wide spectrum of solvent extraction processes utilized for theseparation of polar and non-polar hydrocarbons. No attempt will be madeherein to exhaustively delineate the appropriate published literature;it will suffice to note several examples which are typical of prior artpractices and procedures, and to which the present invention isapplicable. Solvent extraction processes are generally specificallydirected to the recovery of aromatic hydrocarbons from a mixture thereofwith non-aromatic hydrocarbons. Furthermore, these processes indicate adistinct preference for a water-soluble solvent containing an oxygenatedorganic compound. A review of the prior art indicates that the prevalentsolvent is either a sulfolane-type organic compound, or an alkyleneglycol, and preferably a polyalkylene glycol. Although most prior artprocesses are intended to be utilized in conjunction with either ofthese organic solvents, special techniques do exist which are peculiareither to one, or the other.

US. Pat. No. 3,l73,966 (Cl. 260-674) incorporates rectification of richsolvent side-out vapors, withdrawn from the stripping zone, in order torecover substantially solvent-free water for subsequent utilizationwithin the process.

In US. Pat. No. 3,396,101 (Cl. 208-313), a mixture of feed stock andlean solvent is introduced into the stripping column, from which anon-aromatic overhead is withdrawn and introduced into an extractionzone. The resulting rich solvent is passed from the extraction zone tothe stripping column as a second feed stream thereto. US. Pat. No.3,436,435 (Cl. 260-674) involves the utilization of an entrainmentseparator into which the sidecut aromatic stream from the solventstripping zone is introduced.

Still another variation is that found in US. Pat. No. 3,723,256 (Cl.203-43). Initially, the aromatic hydrocarbon feed is introduced into adistillation column from which is recovered a light fraction and aheavier bottoms fraction. The former is passed into an extractivedistillation tower, while the latter is introduced into a liquidextraction unit. The extract from the liquid extraction unit is strippedof non-aromatic hydrocarbons to produce a non-aromatics free fractionand a nonaromatics containing fraction. The aromatics recovered inadmixture with the solvent, from the extractive distillation tower, arepassed to a recovery section in admixture with the aromatic-containingfraction from the stripping zone. The overhead stream from theextractive distillation column and the non-aromatics from the strippingzone are passed in admixture to the bottom section of the solventextraction zone,-to function therein as a reflux stream.

Upon perusal of the foregoing illustrations of prior art solventextraction processes, it will be noted that the improvements affordedthereby result primarily from a variety of modifications with respect tothe internal flow of various process streams. That is, a commoncharacteristic of the multitude of solvent extraction processes is theutilization of at least a solvent extraction zone and a solventstripping zone. For a given solvent extraction unit, designed to processa given quantity of mixed hydrocarbon feed, these two vessels, and therequired manifolding and vessels appurtenant thereto, are the principalfactors contributing to both erection and operating costs. it may besaid, therefore, that economically attractive innovations relate tovarious techniques utilized with respect to the internal flow of variousprocess streams. The resulting economical enhancement generally stemsfrom improved and/or simplified unit operation, lower operating andutility costs, improved product purity, increased solvent recovery,lower overall initial capital investment, etc. The technique encompassedby my inventive concept is applicable to the foregoing describedprocesses, and affords the indicated advantages therein.

OBJECTS AND EMBODIMENTS A principal object of my invention is tosimplify the internal flow of various process streams in a solventextraction unit.

Another object is directed toward the in-process production of steam,substantially free from non-polar hydrocarbons, for internal utilizationin the solvent stripping zone. A corollary objective resides in animprove ment in the purity of the desired polar hydrocarbon product.

Specifically, my invention affords significant economic advantages whenintegrated into currently practiced solvent extraction systems for theseparation and recovery of polar hydrocarbons from mixtures thereof withnon-polar hydrocarbons,

Therefore, in one embodiment, my invention involves a process for therecovery of polar hydrocarbons from a mixture thereof with non-polarhydrocarbons, wherein: (i) said mixture is contacted with awatersoluble, oxygen-containing solvent, selective for the extraction ofsaid polar hydrocarbons; (ii) there is recovered an extract streamcontaining polar hydrocarbons and a major proportion of saidwater-soluble solvent, and a raffinate stream containing non-polarhydrocarbons and a minor proportion of said water-soluble solvent; (iii)said raffinate stream is contacted with water to recover said solventand to provide a hydrocarbon concentrate substantially free from saidsolvent; and, (iv) said extract stream is contacted with steam, in asolvent stripping zone, to remove hydrocarbons from said water-solublesolvent and to recover substantially solvent-free polar hydrocarbons, inwhich process the method of internally preparing steam, substantiallyfree from non-polar hydrocarbons, for use in said solvent strippingzone, comprises the steps of: (a) contacting said raffinate stream witha first water stream to provide a second raffinate stream, substantiallyfree from solvent, and a second water stream containing solvent and aminor quantity of non-polar hydrocarbons; (b) admixing said second waterstream with a first polar hydrocarbon-rich stream and separating theresulting mixture to provide a second polar hydrocarbon streamcontaining non-polar hydrocarbons and a third water stream substantiallyfree from non-polar hydrocarbons; (c) introducing said extract streaminto the upper portion of said solvent stripping zone; (d) generatingsteam into a lower portion of said solvent stripping zone; and, (e)recovering, from said stripping zone, an overhead stream comprisinghydrocarbons, steam and solvent, an aqueous extract stream rich in polarhydrocarbons and a bottoms solvent-rich stream.

These, as well as other objects and embodiments of my invention, willbecome evident from the following detailed description thereof. Withrespect briefly, however, to other such other embodiments, these involveoperating conditions, particular solvents for utilization in theextraction zone, in-process separations and stream flows, etc. Forexample, the aqueous extract, rich in polar hydrocarbons, recovered fromthe solvent stripping zone, is separated to provide a water concentrateand a polar hydrocarbon concentrate, and said raffinate stream iscontacted with at least a portion of the water concentrate as the firstwater stream.

SUMMARY OF INVENTION As hereinafter set forth, the technique encompassedby my inventive concept is intended to be integrated into a solventextraction process for the selective separation and recovery of polarhydrocarbons from a mixture thereof with non-polar hydrocarbons.Although thus applicable to a multitude of hydrocarbon mixtures, furtherdiscussion will be limited to the separation and recovery of aromatichydrocarbons from a mixture thereof with paraffms and/or naphthenes.Initially, the mixture of hydrocarbons is contacted with awater-soluble, oxygen-containing solvent particularly selective for theextraction of the polar hydrocarbons. There is recovered, from thesolvent extraction zone, an extract stream containing aromatichydrocarbons and a major proportion of the water-soluble solvent, and araffinate stream containing non-aromatic hydrocarbons and a relativelyminor proportion of the watersoluble solvent. The raffinate stream isgenerally contacted, in countercurrent flow, with water to recover thesolvent and to provide a hydrocarbon concentrate substantially free fromsolvent. The extract stream is countercurrently contacted with steam ina solvent stripping zone, to remove hydrocarbons from the water-solublesolvent and to recover substantially solvent-free aromatic hydrocarbons.As hereinbefore set forth, the present invention encompasses a method ofinternally preparing the steam utilized in the solvent stripping zone,said steam being substantially free from non-aromatic hydrocarbons.

in accordance with the terminology employed in describing and claimingthe present invention, the raffinate stream recovered from the solventextraction zone is sometimes herein referred to as a first raffinatestream. The first raffinate stream, containing a minor proportion ofboth water-soluble solvent and aromatic hydrocarbons, is introduced intoa lower portion of a water-wash column wherein it is contacted with afirst water stream in countercurrent flow. This water-wash step providesa second raffinate stream which is substantially free from water-solublesolvent, and contains only a minor proportion of aromatic hydrocarbons.The first water stream is substantially free from solvent, but containssome entrained aromatic hydrocarbons. A

second water stream containing solvent and nonaromatic hydrocarbons iswithdrawn from a lower portion of the water-wash zone, admixed with asubstantially pure first aromatic-rich stream (at least about 95.0 mol.percent) and introduced into a separation zone. Separation is effectedto provide a second aromatic stream containing non-aromatic hydrocarbonsand a third water stream containing solvent and a minor quantity ofaromatic hydrocarbons, but being substantially free from non-aromatichydrocarbons (less than about 0.05 mol. percent). It is this third waterstream which is utilized to generate the steam employed in the solventstripping zone.

As in prior art processes, some of which have been previously described,the solvent recovered from the lower portion of the solvent strippingzone is recycled within the process to the solvent extraction zone. Theoverhead stream from the solvent stripping zone, principally comprisinghyrocarbons, steam and solvent vapors, is preferably admixed with theaforesaid second aromatic stream, the mixture being introduced into aso-called stripper receiver. A hydrocarbon stream is withdrawn from thestripper receiver and utilized as backwash in the solvent extractionzone. Also withdrawn from the stripper receiver is a fourth water streamcontaining some solvent and a minor proportion of hydrocarbons. In apreferred embodiment, this fourth water stream is admixed with theaforesaid second water stream and introduced into the separation zone inadmixture with the first, substantially pure aromatic stream.

The comparatively solvent-free, aromatic-rich extract phase iswithdrawn, as a principally vaporous phase from a central portion of thesolvent stripping zone, and is generally subjected to entrainmentseparation for the purpose of removing a greater proportion of theentrained liquid phase, rich in solvent, therefrom. The entrainmentseparation zone may be mechanically arranged within the solventstripping column, or take the form of a separate vessel externally. Theseparated entrained liquid phase is returned to the solvent strippingzone; the balance of the extract phase is condensed and introduced intoan extract receiver for the separation thereof into an aromatic-richproduct stream and a water concentrate. In preferred embodiments, ashereinafter indicated in the description of the accompanying drawing, atleast a portion of the aromatic-rich product stream is utilized as thefirst aromatic stream in admixture with the second water stream. Also,the water concentrate is recycled within the process as the first waterstream introduced into the raffinate water-wash zone. Principal amongthe multitude of advantages, attendant the foregoing describedtechnique, is the production of a high purity steam, substantially freefrom non-aromatic hydrocarbons, thereby significantly reducing theutility requirements of the overall process. A corollary advantageresides in the fact that a lesser quantity of non-aromatic hydrocarbonsis introduced into the solvent stripping zone and, therefore, thearomatic purity of the ultimate product is increased. The overallprocess enjoys a simplified flow scheme resulting in lower capitalinvestment and subsequent operating cost.

SOLVENTS AND OPERATING CONDITIONS Generally accepted solvents, havingsolubility selectivity for aromatic hydrocarbons, are water-soluble,

oxygen-containing organic compounds. Thus, one particularly preferredcategory of suitable solvents are those containing, in general, at leastone molar substituent selected from such radicals as hydroxyl, amino,cyano, carboxyl or nitro radicals. In order to be effective in a systemof extraction such as the process provided by the present invention, thesolvent component having the polar radical must have a boiling pointsubstantially greater than the boiling point of water, added to thesolvent composition for enhancing its selectivity, and, in general, mustalso have a boiling point substantially greater than the end boilingpoint of the hydrocarbon feed stock. In most instances, the solventcomposition has a greater density than the hydrocarbon feed stock and isaccordingly introduced into the uppermost portion of the solventextraction zone, thereafter flowing downwardly, countercurrent to therising hydrocarbon feed stock introduced into the extraction zone at itsmid-point or in the lower portion thereof.

Organic compounds suitable as the solvent component of the solventcomposition may be selected from the relatively large group of compoundscharacterized generally as oxygen-containing compounds, particularly thealiphatic and cyclic alcohols, the glycols and glycol ethers, as well asthe glycol esters and glycol ether-esters. The monoand polyalkyleneglycols in which the alkylene group contains from 2 to 4 carbon atoms,such as ethylene glycol, diethylene glycol, triethylene glycol andtetraethylene glycol, propylene glycol, dipropylene glycol, andtripropylene glycol, as well as the methyl, ethyl, propyl and butylethers of the glycol hydroxyl groups, and the acetic acid estersthereof, constitute a particularly preferred class of organic solventsuseful in admixture with water as the solvent composition of the presentprocess. Various phenols such as phenol and resorcinol and their alkylethers, such as para-cresol, etc., are also effective solvents foraromatic hydrocarbons. Certain aliphatic nitriles, cyano-substitutedethers and amines, such as acetonitrile, and the diethers andpolyalkylene polyamines constitute another group of useful solvents.

Another particularly suitable class of selective solvents are thosecommonly referred to as the sulfolanetype. By this, I intend a solventhaving a 5-membered ring, one atom of which is sulfur, the other fourbeing carbon and having two oxygen atoms bonded to the sulfur atom. Manyof these solvents may be illustrated by the following structuralformula:

wherein R R R and R are independently selected from the group consistingof a hydrogen atom, an alkyl group having up to 10 carbon atoms, analkoxy radical having up to 8 carbon atoms and an arylalkyl radicalhaving up to 12 carbon atoms. Other solvents preferably included are thesulfolenes such as 2-sulfolene or 3-sulfolene which have the followingstructure:

The sulfolane solvents may be made by condensing a conjugated diolefinwith sulfur dioxide and then subjecting the resulting product tohydrogenation, alkylation, hydration and/or other substitution oraddition reactions. Other solvents which have high selectivity forseparating aromatics from non-aromatic hydrocarbons are2-methylsulfolane, 2,4-dimethylsulfolane, methyl 2-sulfonyl ether,n-ary1-3-su1fonyl amine, 2-sulfonyl acctate.

The aromatic selectivity of the selected solvents can be furtherenhanced by the addition of water. Preferably, the solvent contains asmall amount of water dissolved therein to increase the selectivity ofthe solvent phase for aromatic hydrocarbons over non-aromatichydrocarbons without reducing substantially the solubility of thesolvent phase for aromatic hydrocarbons. The presence of water in thesolvent composition provides a relatively volatile material thereinwhich is distilled from the fat solvent in the extractive stripper tovaporize the last traces of non-aromatic hydrocarbon from the fatsolvent stream by steam distillation. The solvent composition containsfrom about 0.5 percent to about 25.0 percent by weight of water, andpreferably from about 3.0 percent to about 15.0 percent depending on theparticular solvent utilized and the process conditions under which theextractor and solvent stripper are operated. By the inclusion of waterin the solvent composition, the solubility of aromatic hydrocarbons inthe solvent, although somewhat reduced in comparison with a non-aqueoussolvent, greatly decreases the solubility of raffinate components in thesolvent and also reduces the solubility of solvent in the raffinatestream. Although the quantity of solvent in the raffinate at any instantis relatively small, the cumulative effect of such small amounts ofsolvent in a stream removed from the process flow and thus otherwiselost, greatly reduces the efficiency and economy of the solventextraction process. Accordingly, it is essential that the solventdissolved in the raffinate stream be recovered therefrom. Such recoverycan be accomplished efficiently by countercurrently washing theraffinate with water in a separate washing zone from which an aqueouswash effluent is recovered containing the solvent recovered from theraffinate.

The solvent extraction zone is operated at elevated temperature and at asufficiently elevated pressure to maintain the feed stock, solvent andbackwash streams in the liquid phase. Suitable temperatures are withinthe range of from 80 to about 400F. and preferably at an intermediatelevel from about 175 to about 300F. Suitable pressures are within therange of about atmospheric pressure up to about 400 psig. and preferablyfrom about 50 psig. to about 150 psig. Generally, the volume of backwashintroduced into the lower point in the extractor is at least percent byvolume of the extract phase leaving the extractor.

The solvent stripper is operated at moderate pressures and sufficientlyhigh reboiler temperatures to drive all the backwash non-aromaticcomponents and some of the aromatics, water and solvent overhead.Typical stripper pressures are from atmospheric to about 100 psig.,although the top of the stripper is generally maintained at from about1.0 psig. up to about psig. The reboiler temperature is primarilydependent upon the composition of the solvent, including its watercontent. Generally, stripper bottom temperatures of from 275 to about360F. are satisfactory.

Other operating conditions will be given in conjunction with thedescription of several embodiments of the present invention asillustrated in the accompanying drawing. Miscellaneous appurtenances,not believed required, by those possessing the requisite expertise inthe appropriate art, have been eliminated from the drawing. The use ofdetails such as pumps, compressors, controls and instrumentation,heat-recovery circuits, valving, start-up lines and similar hardware,etc., is well within the purview of one skilled in the art. It isunderstood that the illustration does not limit my invention beyond thescope and spirit of the appended claims.

DESCRIPTION OF DRAWlNG With reference now to the drawing, it will benoted that the solvent extraction zone has been eliminated. As iswell-known in solvent extraction processes, several examples of whichhave been previously set forth, the selected solvent (in aqueoussolution) countercurrently contacts the mixed hydrocarbon feed andproduces a solvent-rich extract phase predominating in aromatichydrocarbons and a solvent-lean raffinate phase rich in non-aromatichydrocarbons. With reference now to the drawing, the extract phase isintroduced via line 12, and the raffinate phase, containing minorquantities of solvent and aromatics is introduced via line 1. Thesolvent content of the raffinate phase is typically in the range of 1.0percent to 5.0 percent, by weight.

For the purposes of illustration, the feed to the solvent extractionzone will be considered a hexane-plus concentrate resulting from thecatalytic reforming of a naphtha boiling range fraction. The solvent,containing about 6.0 percent by weight of water, is tetraethyleneglycol. The charge stock contains, on a weight bases, 53.0 percent ofaromatic hydrocarbons, 42.0 percent of paraffms and 5.0 percent ofnaphthenes. The resulting raffinate phase contains 2.1 percent by weightof solvent and 2.3 percent aromatics, while the extract phase contains80.8 percent solvent and 19.2 percent hydrocarbons.

The raffinate from the extraction column, herein referred to as thefirst raffinate stream, is introduced, via line 1, into a water-washcolumn 2, wherein it countercurrently contacts a first water stream inline 3. A second raffinate stream containing some aromatic hydrocarbons,about 2.35 percent by weight, and substantially free from tetraethyleneglycol, is recovered via line 4. The use of the term substantially free,with reference to the second raffinate stream, is intended to connotethat the same contains less than about 0.05 percent by weight ofsolvent. A second water stream, containing solvent and non-aromatics, inamounts of 12.3 percent and about 0.2 percent, respectively, is removedfrom the lower portion of water-wash column 4 via line 5, is admixedwith a substantially pure, first aromatic concentrate from line 6, andcontinues via line 5 into separation zone 8.

A second aromatic-rich stream, containing virtually all thenon-aromatics which had been introduced into separation zone 8 with thesecond water stream in line 5, is withdrawn by way of line 10. A thirdwater stream containing 12.3 percent solvent, 0.05 percent aromatichydrocarbons, and substantially completely free (less than 0.01 percentby weight) from non-aromatic hydrocarbons, is removed via line 9 andintroduced thereby into steam generator 11. Steam is generated from thethird water stream through the utilization of the extract phase,withdrawn from the initial solvent extraction zone, as the heat-exchangemedium in line 32. The extract phase continues through line 12 into theupper portion of solvent stripper 13. Steam, along with a minor amountof solvent, is introduced into a lower portion of the solvent strippervia line 14, and water and solvent enter by way of line 15. Recoveredsolvent is recycled to the solvent extraction zone via line 16. In atypical unit, at least a portion of the recovered solvent is diverted toa solvent regeneration facility. It is understood that such a techniqueis not an essential feature of my inventive concept.

The aromatic-rich stream, containing about 2.5 percent of entrainedsolvent and about 0.2 percent by weight of vaporized solvent, 9.3percent water vapor, is withdrawn from an intermediate section ofsolvent stripper 13 by way of line and, following removal of entrainedliquid in entrainment separator 21, through line 23, is introducedthrough line 22 into extract receiver 24. The final aromatic productstream, greater than 99.5 percent pure, is recovered in line 25.Preferred techniques include utilizing at least a portion of the waterremoved in extract receiver 24 as the first water stream to water-washcolumn 2, and at least a portion of the aromatic product as the firstsubstantially pure aromatic stream in line 6.

The overhead stream from solvent stripper 13 is introduced via line 17into stripper receiver 18, in admixture with the second aromatic streamin line 10. A hydrocarbon stream, containing 87.2 percent aromatics and12.8 percent non-aromatics, is recovered in line 19, and is suitable foruse as the backwash stream in the solvent extraction zone. A fourthwater stream is recovered in line 7, and is preferably admixed with thesecond water stream in line 5 for introduction into separation zone 8.

The foregoing specification, and especially the description of theaccompanying drawing, clearly illustrates the method by which thepresent invention is put to advantageous use in the solvent extractionprocess.

I claim as my invention: 7

1. in a process for the recovery of polar hydrocarbons from a mixturethereof with non-polar hydrocarbons, wherein:

i. said mixture is contacted with a water-soluble, oxygen-containingsolvent, selective for the extraction of said polar hydrocarbons;

ii. there is recovered an extract stream containing polar hydrocarbonsand a major proportion of said water-soluble solvent, and a raffinatestream containing non-polar hydrocarbons and a minor proportion of saidwater-soluble solvent;

iii. said raffmate stream is contacted with water to recover saidsolvent and to provide a hydrocarbon concentrate substantially free fromsaid solvent; and,

iv. said extract stream is contacted with steam, in a solvent strippingzone, to remove hydrocarbons from said water'soluble solvent and torecover substantially solvent-free polar hydrocarbons; the method ofinternally preparing steam, for use in said solvent stripping zone,substantially free from nonpolar hydrocarbons, which method comprisesthe steps of:

a. contacting said raffinate stream with a first water stream to providea second raffinate stream, substantially free from solvent, and a secondwater stream containing solvent and a minor quantity of non-polarhydrocarbons;

b. admixing said second water stream with a first polar hydrocarbon-richstream and separating the resulting mixture to provide a second polarhydrocarbon stream containing non-polar hydrocarbons and a third waterstream substantially free from non-polar hydrocarbons;

c. introducing said extract stream into the upper portion of saidsolvent stripping zone;

01. generating steam from said third water stream and introducing saidsteam into a lower portion of said solvent stripping zone;

e. recovering, from said stripping zone, an overhead stream comprisinghydrocarbons, steam and solvent, an aqueous extract stream rich in polarhydrocarbons and a bottoms solvent-rich stream;

f. commingling said overhead stream with said second polar hydrocarbonstream and separating the resulting mixture to provide a fourth waterstream and a hydrocarbon-rich stream; and

g. commingling said fourth water stream with said second water streamand said first polar hydrocarbon-rich stream.

2. The method of claim 1 further characterized in that saidwater-soluble solvent is a sulfolane-type organic compound.

3. The method of claim 1 further characterized in that saidwater-soluble solvent is a polyalkylene glycol.

4. The method of claim 1 further characterized in that said aqueousextract stream is separated to provide a water concentrate and a polarhydrocarbon concentrate.

5. The method of claim 4 further characterized in that said raffinatestream is contacted with at least a portion of said water concentrate assaid first water stream.

6. The method of claim 4 further characterized in that at least aportion of said polar hydrocarbon concentrate is admixed with saidsecond water stream as said first polar hydrocarbon-rich stream.

7. The method of claim 1 further characterized in that said polarhydrocarbons are aromatic.

8. The method of claim 1 further characterized in that said non-polarhydrocarbons comprise naphthenes.

1. IN A PROCESS FOR THE RECOVERY OF POLAR HYDROCARBONS FROM A MIXTURETHEREOF WITH NON-POLAR HYDROCARBONS, WHEREIN: I. SAID MIXTURE ISCONTACTED WITH A WATER-SOLUBLE, OXYGENCONTAINING SOLVENT, SELECTIVE FORTHE EXTRACTION OF SAID POLAR HYDROCARBONS; II. THERE IS RECOVERED ANEXTRACT STREAM CONTAINING POLAR HYDROCARBONS AND A MAJOR PROPORTION OFSAID WATERSOLUBLE SOLVENT, AND A RAFFINATE STREAM CONTAINING NONPOLARHYDROCARBONS AND A MINOR PROPORTION OF SAID WATERSOLUBLE SOLVENT; III.SAID RAFFINATE STREAM IS CONTACTED WITH WATER TO RECOVER SAID SOLVENTAND TO PROVIDE A HYDROCARBON CONCENTRATE SUBSTANTIALLY FREE FROM SAIDSOLVENT; AND, IV. SAID EXTRACT STREAM IS CONTACTED WITH STEAM, IN ASOLVENT STRIPPING ZONE, TO REMOVE HYDROCARBONS FROM SAID WATERSOLUBLESOLVENT AND TO RECOVER SUBSTANTIALLY SOLVENT-FREE POLAR HYDROCARBONS;THE METHOD OF INTERNALLY PREPARING STEAM, FOR USE IN SAID SOLVENTSTRIPPING ZONE, SUBSTANTIALLY FREE FROM NON-POLAR HYDROCARBONS, WHICHMETHOD COMPRISES THE STEPS OF: A. CONTACTING SAID RAFFINATE STREAM WITHA FIRST WATER STREAM TO PROVIDE A SECOND RAFFINATE STREAM, SUBSTANTIALLYFREE FROM SOLVENT, AND A SECOND WATER STREAM CONTAINING SOLVENT AND AMINOR QUANTITY OF NON-POLAR HYDROCARBONS; B. ADMIXING SAID SECOND WATERSTREAM WITH A FIRST POLAR HYDROCARBON-RICH STREAM AND SEPARATING THERESULTING MIXTURE TO PROVIDE A SECOND POLAR HYDROCARBON STREAMCONTAINING NON-POLAR HYDROCARBONS AND A THIRD WATER STREAM SUBSTANTIALLYFREE FROM NON-POLAR HYDROCARBONS; C. INTRODUCING SAID EXTRACT STREAMINTO THE UPPER PORTION OF SAID SOLVENT STRIPPING ZONE; D. GENERATINGSTEAM FROM SAID THIRD WATER STREAM AND INTRODUCING SAID STEAM INTO LOWERPORTION OF SAID SOLVENT STRIPPING ZONE; E. RECOVERING, FROM SAIDSTRIPPING ZONE, AN OVERHEAD STREAM COMPRISING HYDROCARBONS, STEAM ANDSOLVENT, AN AQUEOUS EXTRACT STREAM RICH IN POLAR HYDROCARBONS AND ABOTTOMS SOLVENT-RICH STREAM; F. COMMINGLING SAID OVERHEAD STREAM WITHSAID SECOND POLAR HYDROCARBON STREAM AND SEPARATING THE RESULTINGMIXTURE TO PROVIDE A FOURTH WATER STREAM AND A HYDROCARBON-RICH STREAM;AND G. COMMINGLING SAID FOURTH WATER STREAM WITH SAID SECOND WATERSTREAM AND SAID FIRST POLAR HYDROCARBON-RICH STREAM.
 2. The method ofclaim 1 further characterized in that said water-soluble solvent is asulfolane-type organic compound.
 3. The method of claim 1 furthercharacterized in that said water-soluble solvent is a polyalkyleneglycol.
 4. The method of claim 1 further characterized in that saidaqueous extract stream is separated to provide a water concentrate and apolar hydrocarbon concentrate.
 5. The method of claim 4 furthercharacterized in that said raffinate stream is contacted with at least aportion of said water concentrate as said first water stream.
 6. Themethod of claim 4 further characterized in that at least a portion ofsaid polar hydrocarbon concentrate is admixed with said second waterstream as said first polar hydrocarbon-rich stream.
 7. The method ofclaim 1 further characterized in that said polar hydrocarbons arearomatic.
 8. The method of claim 1 further characterized in that saidnon-polar hydrocarbons comprise naphthenes.